15in Up Gunned Gneisenau v 1939 Modernized Renown

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lwd
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by lwd »

Dave Saxton wrote:That seems quite a stretch to me. Last I checked NC has a 1 1/2-inch upper deck just as described in the document. NC was the new battleship at the time of the document. 1936 is plenty early enough to work these findings into the design. The bomb deck idea makes a nice cover when such matters were still highly classified though . But a 38mm bomb deck doesn't function as such very well in practice.
I see it the other way around. Indeed the choice of the thickness looks to me like it was based on the design. If someone has a reference for the preliminary designs it would be pretty easy to tell. Why do you think 38mm won't work well as a bomb deck by the way?
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Dave Saxton
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by Dave Saxton »

I can't tell you how to interput, but I don't think this really a matter of interputation. The USN BoO themselves plainly state what the 38mm plate was and it's intended purpose:
in connection with the design of the protective decks of the new battleships. Extensive tests were made with the view of utilizing a 1 ½-inch main deck as a yaw plate for major caliber A. P. projectiles
It's usefulness as a bomb deck are rather limited against bombs striking at or near the normal, which bombs usually do. At the normal, the 38mm plate will not consume enough energy to really protect the main deck from a bomb. If the bomb's kenetic energy is so low that it would be significantly slowed, then it doesn't really pose a threat to the main armoured deck anyway. Most of this weight would probably be better just put into the main plate if AP bombs are the threat. If the bomb is so light cased as to be broken up by the 38mm plate it would certainly pose no threat to the main armour that is only about 2 .5 meters below anyway. It would initiate the action of a delay action fuse, but since the space between the two armoured decks is only one deck level, this fact doesn't matter very much. For the bomb to explode before reaching the main armoured deck it would need to be going extremely slow or have an extremely short fuse delay. In that case the bomb will once again pose no threat to the main armour. The USN's own description of the deck's designed function make far more sense.
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by Bgile »

Dave,

I think a "bomb deck" might be to cause an HE type bomb to explode on the upper deck rather than internally in the ship. Is this a possible explanation?

I agree that it does seem to be a yaw deck by design, but obviously it could serve other purposes.
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Dave Saxton
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by Dave Saxton »

Agreed.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by dunmunro »

Bgile wrote:Dave,

I think a "bomb deck" might be to cause an HE type bomb to explode on the upper deck rather than internally in the ship. Is this a possible explanation?

I agree that it does seem to be a yaw deck by design, but obviously it could serve other purposes.
I think a "bomb deck" is designed to initiate fuse action of SAP or AP bombs and maybe detonate or break up GP/HE bombs. This would force the use of SAP or AP bombs which are less likely to do damage (from near misses, for example) if they do not penetrate.
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by lwd »

dunmunro wrote: ... I think a "bomb deck" is designed to initiate fuse action of SAP or AP bombs and maybe detonate or break up GP/HE bombs. This would force the use of SAP or AP bombs which are less likely to do damage (from near misses, for example) if they do not penetrate.
This is my understanding as well. In addition to initiating the fuse it might also slow down the bomb enough that it wouldn't pentrate into the vitals. One can get extra penetration by releasing at a greater altitude but you give up accuracy that way. My understanding is that one of the things that determined the altitude of the Japanese level bombers at PH was the estimated velocity and subsequent height required for them to penetrate into the vitals of the US BBs. Consider also in that regard that they were using a specially built bomb.
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Dave Saxton
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Re: 15in Up Gunned Gneisenau v 1939 Modernized Renown

Post by Dave Saxton »

In that case a bomb deck as in the NC class would provide only marginal additional protection, because of the finite distance between the two armoured decks striking at or near the normal. Luftwaffe studies of light upper armoured decks on battleships determined that it would only reduce the velocities of large caliber bombs 5-10% when they struck at or near the normal. It would require that the bomb be dropped from a slightly higher altitude if the altitude was calculated to provide the necessary velocity to defeat the main armour, however.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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